Synthesis and properties of novel fluorotelechelic macrodiols containing vinylidene fluoride, hexafluoropropene and chlorotrifluoroethylene

The dead-end radical copolymerization of 1,1-difluoroethylene (or vinylidene fluoride, VDF or VF2) with hexafluoropropene (HFP) initiated by hydrogen peroxide for obtaining original fluorinated telechelic elastomers is presented. The influence of the process (solution or emulsion) and the nature and amounts of solvents were studied, Various initial [H2O2](i)/[fluoroolefins](i) molar ratios, ranging from 5 to 40%, were used, showing that the higher the hydrogen peroxide amount, the lower the molecular weights of the polymers obtained leading to fluorinated telechelics. Hence, low molecular weight copolymers, the (M-n) over bar Mn of which ranged from 800 to 3200, were synthesized. A careful structural analysis of these fluorinated telechelics was performed and enabled one to determine the fluorinated base units of both alkenes in the copolymers. Interestingly, these liquid to oily products exhibited low glass transition temperatures (from -80 to -40 degreesC). The mechanism of the reaction was approached and showed that the hydroxyl radical generated from hydrogen peroxide reacted to the hydrogenated carbon atoms of VDF but also to the fluorinated carbons of VDF and HFP, yielding COOH end groups, and is discussed. The selective reduction of these carboxylic end groups was achieved in the presence of lithium aluminum hydride leading to fluorinated telechelic diols.